This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Over the past 30 y the prevalence of overweight children (6-19 y) in the USA (BMV>95th percentile) has increased 3-fold to reach 16% in 2000 (NHANES). Concomitant with the increase in childhood overweight, the incidence of type 2 diabetes in children (0-19 y) has increased 4-fold. Although the etiology of obesity related impairement of glucose metabolism is multifactorial, dietary macronutrient intake and physical activity are potentially important factors. The aims of this proposal are to determine in healthy adolescents 1) the impact of obesity on energy expenditure and substrate oxidation, glucose production from gluconeogenesis and glycogenolysis, insulin secretion and sensitivity, and lipolysis;2) whether a 12 weeks resistance training exercise program will improve glucose metabolism in obese adolescents, and if so, 3) whether the exercise effect is correlated with a decrease in total intramyocellular, visceral and/or hepatic fat content. To address these questions, 12 over weight (body fat >30%) and 12 lean (body fat <25%) adolecents will be studied on two occasions (just prior to the start of a 12 weeks exercise program and at the end of the last week of exercise);in all subjects, each of the two study occasions will be preceded by 7-d of a high fat diet. State of the art stable isotope-GCMS techniques and MRI will be sued to obtain the data needed to address the aims stated above. The information provided by these studies will improve our understanding of the metabolic effects of obesity in adolescents, will lead to identifying factors which may increase, prvent or delay the development of type 2 diabetes. It will also help us determine whether strength exercise without intent to weight loss will improve insulin sensitivity and normalize glucose metabolism in over weight adolescents. Overall hypotheses: Resistance training exercise (without intent of weight loss) improves insulin sensitivity, normalizes glucose metabolism and reduces intramyocellular, visceral and hepatic fat in healthy obese adolescents. Specific hypotheses: H1. A 12 weeks resistance exercise program (x 2/week, 1 h/session) increases insulin sensitivity in obese adolescents, but not in already insulin sensitive lean adolescents.